1. Field of the Invention
The present invention relates to a color conversion method for a color display device, and, more particularly, to a color conversion method which can be used for direct printing by a color display device using a wide-gamut color space.
2. Description of the Related Art
Color display devices using a wide-gamut color space may directly print color image data such as JPEG files without using another device (e.g., a PC), as in the case when a memory card storing a number of images is inserted into a color printer, and the images in the memory card are directly printed by the color printer. This type of printing is referred to as “direct printing”.
In the case of using a direct-printing function provided by a color display device using a wide-gamut color space, YCC data such as JPEG data, which is wide-gamut image data, is converted into RGB data by multiplying the YCC data by a 3×3 matrix and clipping the result of the multiplication to the range of 0 to 255. Thereafter, the RGB data is converted into CMY data using an RGB-to-CMY lookup table (LUT) so as to be able to be printed by a color display device.
FIG. 1 is a diagram for explaining a conventional method of outputting an image using a direct-printing function of a color printer. Referring to FIG. 1, encoded YCC data 12 in a JPEG file 11 created using a camera 10 is converted into RGB data 14 using a 3×3 YCC-to-RGB conversion matrix, as indicated by Equation (1) below.
                              [                                                    R                                                                    G                                                                    B                                              ]                =                              [                                                            1                                                  0                                                  1.402                                                                              1                                                                      -                    0.344136                                                                                        -                    0.714136                                                                                                1                                                  1.772                                                  0                                                      ]                    ⁡                      [                                                            Y                                                                                                  C                    ⁢                                                                                  ⁢                    r                                                                                                                    C                    ⁢                                                                                  ⁢                    b                                                                        ]                                              (        1        )            
Then, the RGB data 14 is converted into data 16 of the CMY color space, which is a color space used by a color printer 17, using an RGB-to-CMY LUT 15. Thereafter, the CMY data 16 is output by the color printer 16.
According to the method of FIG. 1, R, G, and B values resulting from the conversion of image data from the YCC color space to the RGB color space satisfy the following relations: −1.201<R<1.701; −0.529<G<1.529; and −0.886<B<1.886. However, in a conventional method of outputting YCC data, RGB data is all clipped to the range of 0 to 1 prior to the color conversion operation. Thus, it is difficult even for a display device (such as a printer) that supports a wide-gamut color space to properly represent gradations and details of wide-gamut data using a conventional method of outputting YCC data.